Excerpt from Case Histories of Corps Breakwater and Jetty Structures, Vol. 8: Lower Mississippi Valley Region

3. There are 10 projects within LMVD which contain 19 jetty structures (figure There are no breakwaters. All projects are located on the Gulf of Mexico, and of these, eight are situated near the mouth of the Mississippi River (figure With the exception of the single jetty at Grand Isle, all projects have dual jetties. There is a total length of over lin ft of jetty structures. All of these are rubble mound (stone and/or shell) in cross section, with the exception of the jetties at South and Southwest Passes, which have been supplemented with concrete caps on several occasions since original construction. Concrete capping has not been used recently and is not expected to see future use due to its higher cost compared with stone. The structures typically have been built on unconsolidated silts and clays which exist throughout the area to depths of several hundred feet. Most of the structures are located in water depths of less than 10 ft*. (the seaward ends of the jetties at South and Southwest Passes are in water depths of 20 to 30 ft.) Construction of early jetty projects, such as those at South and Southwest Passes, consisted of one to several layers of fascine mats, each layer ballasted with riprap stone, with additional stone added to obtain the desired crest elevation. (significant portions of the Mississippi Passes jetties also were capped with concrete during original construction.) Fascine mats were used as late as 1939 at Southwest Pass, 1942 at Calcasieu Pass, and 1950 at Bayou Fontanelle. Construction of the most recent projects such as Gulf Outlet, Tiger Pass, and Baptiste Collette Bayou, has used shell materials as a bedding and core material, which then is covered with riprap or armor stone. These projects were constructed in two stages, the first being a wide base of shell and riprap stone as mentioned previously, and the second a rubble-mound section typical of jetty structures.

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